Major earthquake in Oregon could be in next 50 years, infrastructure not ready

Oregon's offshore seismic fault mirrors Japan's, called a subduction zone, where one tectonic plate overlaps another. The frictional force of the dragging results in massive energy storage underground, which occasionally releases in a "megathrust" earthquake. Only megathrusts are known to produce earthquakes as high as 9.0.

The threat isn't just the quake's power, however. The Cascadia Subduction Zone will probably cause shaking for 3-5 minutes, said Scott Ashford of OSU, not involved in the study.

A lot of the seismic design standards have been based on quakes of 30 seconds, common in California, and don't account for the extended shaking.

"Oregon is not ready. We have a bunch of legacy infrastructure," said Ashford, "but it's never been tested and was never designed for Cascadia Subduction Zone earthquakes."

Wang says that the greatest risk to the Northwest is liquefaction, where wet, loose soil behaves like a liquid. Buried tanks and pipes can float out of the ground, and buildings can sink. She said that all of the port terminals along Oregon riverbanks are on easily-liquefied soil and that critical infrastructure like electricity and fuel could easily be disrupted.

An Oregon Department of Transportation report from 2009 states that many major roads, including Interstate 5, will be completely impassable following a megaquake because of damage like falling overpasses. As of 2009, 178 of Oregon's 2,567 bridges had received a retrofit for seismic stability, but the Oregon Department of Transportation has no current funding for the program.

Wang said a priority is protecting civic and critical infrastructure. Oregon has a grant program to help fund safety retrofits for schools and emergency facilities. Two weeks ago, seven schools got funding from this program, bringing the statewide total to 22 since 2011. More than 1,000 Oregon schools are at high risk of collapse in a strong earthquake, however. "At that rate we're not going to be able to fix that many schools," said Wang.

In an extreme earthquake, Ashford said, "electricity will be down, roads will be down and you can't go to pharmacy to refill something. Everybody needs to take responsibility to be prepared."

"After every earthquake, people always wish they had done something," said Wang.

On the coast, people could have less than 15 minutes to reach high ground if there's a tsunami.

"I go to the coast, and I enjoy staying in a hotel with my family," said Ashford. But, "I always look: where's my evacuation route?"

The Oregon Department of Geology and Mineral Industries is developing an updated set of tsunami inundation maps to help with evacuation planning, many of which are already available online at the DOGAMI website.

The lack of previous seismic events in Oregon explains some of the state's unpreparedness. "It's enigmatic," says Goldfinger. "Of all the subduction zones in world, the Cascadia Subduction Zone is the quietest that we know of."

"This may come up sooner than we think," he said. "We may not have lots of time to do education and retrofits."